But Catelyn is no longer the woman she was in the books, and so all of her tragedy lacks sting. The writers scrambled to make amends for past mistakes in order to make the scene more powerful, by actually giving her lines, by acknowledging that she gives good advice and that Robb does rely on her, but it was too little, too late. Imagine how much more powerful Catelyn’s plea to “let it end” would be, if we had seen, over an extended period of time, how Catelyn understands the cost of war, how all she wants is for the war to end so that the people she loves can be safe. Imagine how shocking it would be to have her threaten to cut Walder Frey’s wife’s throat, if Catelyn had been shown to be someone who is not all about revenge, who is honorable and kind and would never do something like that unless she was desperate. Imagine what a strong moment it would be when she then cut that innocent girl’s throat, as a woman who’s lost everything, a woman driven to be someone that she’s not because everything has been stolen from her.
— Rhiannon, Game of Thrones: The Rains of Castamere